This invention relates to an improved method of preparing acetal carboxylate polymers which are useful as complexing agents and detergency builders.
The property possessed by some materials of improving detergency levels of soaps and synthetic detergents and the use of such materials in detergent compositions is known. Such cleaning boosters are called "builders" and such builders permit the attainment of better cleaning performance than is possible when so-called unbuilt compositions are used. The behavior and mechanisms by which builders perform their function are only partially understood. It is known that good builders must be able to sequester most of the calcium and/or magnesium ions in the wash water since these ions are detrimental to the detergency process. However, it is difficult to predict which class of compounds possess useful combinations of builder properties and which compounds do not because of the complex nature of detergency and the countless factors which contribute both to overall performance results and the requirements of environmental acceptability.
Acetal carboxylate polymers have been found to be suitable as a builder in detergent formulations. The composition of such acetal carboxylate polymers has been disclosed in U.S. Pat. No. 4,144,226 issued Mar. 13, 1979 and in Ser. No. 962,512 filed Nov. 20, 1978. The use of such acetal carboxylate polymers in detergent compositions is disclosed in U.S. Pat. No. 4,146,495 issued Mar. 27, 1979. A preferred method for the saponification of the esters of the acetal carboxylate polymers to form the corresponding alkali metal salt is disclosed in U.S. Pat. No. 4,140,676 issued Feb. 20, 1979. The acetal carboxylate polymeric salts described in the above applications and patents were tested for sequestration function using the procedures described by Matzner et al in "Organic Builder Salts as Replacements for Sodium Tripolyphosphate," TENSIDE, 10, No. 3, pages 119-125 (1973). As a result of such tests, the polymeric acetal carboxylate salts were found to be superior detergent builders compared to sodium tripolyphosphate and were stable under laundry use conditions but depolymerized at lower pH making the polymers more readily biodegradable.
The acetal carboxylate polymers prepared according to the methods disclosed in the above patents and patent applications provide satisfactory results. However, it was observed that some acetal carboxylate polymers had greater hydrolytic stability than others and it was further observed that the hydrolytic stability was related to the chemically stable group at the polymer termini which stabilized the polymer against rapid depolymerization in alkaline solution. Those skilled in the art would find it desirable to be able to predict the hydrolytic stability of a particular acetal carboxylate polymer, not only to determine whether or not a particular acetal carboxylate polymer would be suitable for use in a particular detergent formulation, but also to determine the usefulness of such acetal carboxylate polymers in applications outside of cleaning and detergency, for example, the deflocculation of kaolin clays.
Now, a relationship has been established between hydrolytic stability and the structure of the particular end groups at the termini of the acetal carboxylate polymer. This relationship permits those skilled in the art to be able to predict which acetal carboxylate polymer will be more hydrolytically stable compared to other acetal carboxylate polymers, permitting the usefulness of such acetal carboxylate polymers to be extended to numerous other applications, both within and outside of the detergency and cleaning field.